共查询到20条相似文献，搜索用时 15 毫秒
1.
《Gondwana Research》2014,25(1):214-225
Jurodidae are thought to be some of the world's most mysterious beetles and display an intriguing mixture of characters occurring in three different suborders. Hitherto, all known fossil and extant Jurodidae were extremely rare and restricted to Russian Siberia and the Far East. Here we describe two new species, Jurodes daohugouensis sp. nov. and Jurodes pygmaeus sp. nov. from the Middle Jurassic of Daohugou, China. A key to all species of Jurodidae and their research history are given, and the detailed morphology of fossil Jurodidae is also presented. Our results confirm the presence of three ocelli in fossil Jurodidae, and reveal that hind wings of J. pygmaeus sp. nov. possess well developed radial and oblong cells, and are very similar to those of extant Jurodidae (Sikhotealinia zhiltzovae). Male genitalia of fossil Jurodidae were described herein for the first time, showing a basal trilobate structure. The presence of exposed propleuron, three pairs of external trochantins, metanepisterna with ridges, primitive characters of wing venation further support the probable placement of Jurodidae in the suborder Archostemata. J. daohugouensis and J. pygmaeus are very similar to S. zhiltzovae in having the big protruding eyes, elevated median portion of frons bearing three ocelli, pubescent body, contiguous procoxae, exposed trachantion of all coxae, elytra with rows of punctures, and wing venation. Our results show that these key characters of extant Jurodidae can be traced back to the Middle Jurassic, revealing that the family has been in a period of evolutionary stasis for at least 160 million years. Furthermore, our discoveries widen the paleogeographic distribution of fossil Jurodidae from Russian Siberia to northern China. 相似文献
2.
Charles Hepworth Holland 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(1):13-23
Coiled nautiloid cephalopods from the British Silurian are described and their taxonomy revised. The Order Oncocerida is represented by a single specimen of Oxygonioceras oxynotum. Twelve species from the Order Tarphycerida (within which is here subsumed the Order Barrandeocerida) are described: one of Trocholites, two of Ophioceras, two of Catyrephoceras, three of Lechitrochoceras, one of Peismoceras, two of Systrophoceras, and one of Uranoceras. Their distribution, stratigraphical and geographical, is indicated. 相似文献
3.
An improved discrete element method based on a variational formulation of the frictional contact law
An improved algorithm based on the contact dynamics approach is proposed. Like previous developed algorithms it involves two stages. In the first one (local stage) for each particle, forces are computed from the relative displacement using an interaction law, which models frictional contact and shock. In the second stage (global stage) Newton's second law is used to determine, for each particle, the resulting acceleration which is then time-integrated to find the new particle positions. This process is repeated for each time step until convergence is achieved. The two distinguishing features of the present algorithm are the local integration of the frictional contact law and the convergence criterion. By adopting a variational statement of the frictional contact law based on the bi-potential concept, the integration procedure is reduced to a single predictor-corrector step and a new convergence criterion is introduced. Both aspects significantly reduce the computing time and enhance the convergence. Numerical applications show the robustness of the algorithm. 相似文献
4.
Quantifying living roots in a marsh is a necessary but difficult task in wetland research. The two main difficulties usually encountered are distinguishing living from dead roots and processing a dense mat of fine roots. We found that living roots of salt-marsh plants release much more dissolved organic carbon (DOC) in boiling water than dead roots. Based on the finding, we developed a DOC procedure to quantify living roots of Spartina alterniflora and Juncus roemerianus. The DOC released in boiling water is a function of root activity, and the amount released can be used to calculate the living root biomass of a sample. The amount of living roots determined by the DOC method correlated well with the amount of living roots determined by the manual, sorting method (r2 = 0.78, p<0.01). The DOC method is more objective, precise, and much less tedious than the manual sorting method. 相似文献
5.
针对高应力软岩公路隧道的特点,对湖北宜巴高速公路峡口隧道开展了地应力测试、隧洞收敛下沉、接触应力、结构受力等项目的监测工作。地应力测试结果表明,虽然隧洞埋深不大,但由于构造应力的存在,仍属于高地应力区。施工监测结果表明,高应力软岩隧道变形与结构受力具有明显的时空效应,与开挖方式、工作面距离以及支护时机密切相关。由于隧洞围岩软弱破碎,加之处于高应力作用下,在工作面通过后,岩体产生持续性的流变变形,导致隧洞产生挤压大变形和结构受力的持续增加,达到支护结构强度极限,最终导致围岩失稳和支护体系的失效。基于上述研究成果,提出了相应的高应力软岩大变形支护设计对策。研究成果为高应力软岩隧道变形与结构受力的时空效应性提供了监测数据支持,为峡口隧道的施工和支护设计提供了依据,对我国西部其他高应力软岩公路隧道的建设具有借鉴意义 相似文献
6.
传统意义的刘岭群广泛分布于南秦岭北缘地区,由于特殊的大地构造位置,其一直被视为揭示秦岭造山带早古生代南秦岭构造带和北秦岭构造带汇聚过程的重要窗口.丹凤－商南－西坪地区的刘岭群较山阳－柞水地区的刘岭群变质程度深且变形复杂,分别被称为刘岭群浅变质沉积岩系和刘岭群沉积岩系以示区分.山阳－柞水地区的刘岭群沉积岩系据可靠的古生物化石证据被划归为中泥盆统或上泥盆统,而商丹地区的刘岭群浅变质沉积岩系则无可靠的时代证据,被划归为下古生界.通过对商丹地区浅变质沉积岩系中的石榴二云母石英片岩进行LA-ICP-MS锆石U-Pb同位素年龄研究,获得碎屑锆石年龄谱介于2 598~390 Ma,2个主要峰值年龄段分别为~1.0~0.6 Ga和~0.5~0.4 Ga,3个次要峰值年龄段分别为~2.6~2.3 Ga、~1.71~1.60 Ga和~1.3~1.2 Ga.综合本次及前人研究结果表明:刘岭群浅变质沉积岩系和沉积岩系物源具有双源性,南、北秦岭构造带均为其提供重要物源;商丹地区刘岭群浅变质沉积岩系最大沉积时限为~390 Ma,该地层最可能形成于中晚泥盆世;刘岭群沉积岩系和刘岭群浅变质沉积岩系可能为同时代沉积物,后期经历不同构造变形,形成于前陆盆地构造环境. 相似文献
7.
A study of the cheirolepidiaceous conifer Pseudofrenelopsis gansuensis from the Lower Cretaceous of Wangqing Jilin Province in China was conducted in detail using scanning and transmission electron microscopy techniques. In total, nine ultrastructural features were recognized for the cuticle of this fossil plant, which are helpful in the distinguishing between cuticles of ordinary epidermal cells, subsidiary cells, guard cells and hypodermal cells of the stomatal apparatus. A three dimensional reconstruction of the cuticle ultrastructure was obtained. Pseudofrenelopsis gansuensis is the second species of this genus for which the cuticle ultrastructure has been statistically examined with 30 measurements and estimated confidence interval values. The close comparison of the cuticle ultrastructure characters, including statistical data, among Cheirolepidiaceae and other fossil conifers provides potential evidence of the taxonomic significance of this genus: ten characters are potentially valuable for specific separation, eleven parameters for generic separation and three parameters seem also to be useful for Family determination. The differences in the chemical composition according to preliminary statistical element analyses of the cuticles based on three ratios in two species of Pseudofrenelopsis, P. dalatzensis and P. gansuensis, should also be examined in future studies. 相似文献
8.
利用中国542个站1960-2003年逐日降水资料,分析中国极端降水事件的区域性和持续性,研究发现:滇西藏东一带极端降水的持续性较好,但该地区极端降水的区域性较差;长江以南地区夏季极端降水的区域性与持续性均较好,容易导致区域性洪涝灾害的发生;东南沿海冬季极端降水的区域性与持续性均较好,易形成成片且持续时间在3d或3d以上的极端(较强)降水事件;黄河中下游秋季极端降水的区域性与持续性均较好,该地区秋季发生洪涝的可能性较大;除新疆以外,东北、华北以及西北等大部分北方地区极端降水的持续性以及区域性均较差。 相似文献
9.
Robin Fentimen Andres Rüggeberg Aaron Lim Akram El Kateb Anneleen Foubert Andrew J. Wheeler Silvia Spezzaferri 《Swiss Journal of Geoscience》2018,111(3):561-572
Cold-water coral ecosystems represent unique and exceptionally diverse environments in the deep-sea. They are well developed along the Irish margin, varying broadly in shape and size. The Moira Mounds, numerous small-sized mounds, are nestled in the Belgica Mound Province (Porcupine Seabight, North-East Atlantic). The investigation of living (Rose Bengal stained) and dead benthic foraminiferal assemblages from these mounds allowed to describe their distribution patterns and to evaluate their response to environmental variability. Quantitative data was statistically treated to define groups of species/genera associated to specific habitats. The Moira Mounds differ from their larger neighbours by the reduced spatial variability of benthic foraminiferal assemblages, living assemblages only distinguishing coral-rich and coral-barren areas. The ecological needs of corals are highlighted by the abundance of Alabaminella weddellensis and Nonionella iridea, phytodetritus-feeding species in coral supporting sediments. Living foraminifera in sediments from the Moira Mounds concentrate in the upper first centimetre. Infaunal species may be affected by bioturbation and/or reworking by the strong currents in the area. Dead foraminiferal assemblages from the Moira Mounds resemble those described for the sandwave facies in adjacent giant mounds, suggesting similar processes in facies deposition. 相似文献
10.
Summary Longwall panel layouts in the USA differ from other countries in that each panel is blocked out at both sides by at least three parallel panel entries separated by chain pillars. The panel entries may vary in width up to 90 m depending on local conditions.A finite element analysis in two and three dimensions of hypothetical longwall prototypes in the Pittsburg seam, where significant tailentry closure has been reported was carried out. This showed that convergence of tail and head entries undergoes cyclic variation, the period of which depends on the strength and thickness of competent roof layers and their location relative to the face geometry. The panel width was found to have a particular effect on the period and amplitude of potential cyclic phenomena. 相似文献
11.
Seafloor elastic parameters are important for seafloor engineering and geophysical detection beneath the seafloor. We have proposed to use AVO (amplitude variation with offset) theory to estimate seafloor elastic parameters. However, the previous inversion methods are time-consuming. To improve the computing efficiency, we try to solve the inverse problem as an unconstrained optimization problem in this paper. Three kinds of classical unconstrained optimization methods are applied to seafloor AVO inversion, including the steepest descent method, the Newton’s method, and the conjugate gradient method. Then, we design different initial models to test the convergence behaviors of the three methods. Numerical tests show that the perturbation level of the initial models and the noise level of the observed data have a significant effect on the convergence performances of the three methods. Even for the same perturbation and noise levels, the convergence performances differ with different combinations of the perturbed initial elastic parameters. All three methods have higher computing efficiency than the previous methods. This research also offers a strategy to choose a proper optimization method for a specific case in real seafloor AVO inversion. 相似文献
12.
记贵州顶效中三叠世一新的海生爬行动物 总被引：7，自引：0，他引：7
在贵州兴义顶效绿荫村西大约150m绿荫水泥厂南面采石场出露的中三叠统杨柳并组（拉丁阶）灰黑色中薄层灰岩中发现一新的海生爬行动物－绿荫顶效龙Dingxiaosaurus luyinensisgen.et sp.nov。它的肢骨形态和结构颇为独特，股骨，胫，腓骨以及跗骨的形状和结构相似于原始的鱼龙，而趾骨形状和数目有些相似于最早的蛇颈龙，但又与所有已知的鱼龙和蛇颈类类的属种均明显不同，它是早期海生爬行动脉进化的一个比较原始而孤立的新种类，它的发现对早期海生爬行动物进化多样性的认识具有十分重要的科学意义。 相似文献
13.
广西河池北香银多金属矿床同沉积断层的厘定及其发现意义 总被引：2，自引：1，他引：1
广西河池北香银多金属矿床已经进行了20多年的找矿勘探,基本探明了1～6号脉状矿体,但在找矿理论、矿床资源量上均未能取得实质性的突破,矿床资源也因此未能获得开发利用.通过工作,在矿区内发现了一组具有长期持续活动并控制着矿区内的沉积作用和后期构造活动特征的北西向同沉积断层,已知矿体的产状、空间分布均明显受到该同沉积断层的控制,因此该组构造具有控岩控矿特征.对比显示本矿区同沉积断层与大厂矿田的同沉积构造及其控矿特征具有相似性,在该组同沉积断层的上盘尤其与南北向、北东向构造交汇的部位是成矿的有利地段,脉状矿体的下部可能存在层状矿体.该组同沉积断层的发现开拓了北香地区找矿思路,为今后找矿勘探指明了方向. 相似文献
14.
<正>Three lepidopteran species,from the Middle Jurassic Daohugou beds(inner Mongolia,China),are described in a new family,Mesokristenseniidae,and new genus,Mesokristensenia,which could represent the sister group of the Micropterigidae.Mesokristensenia differs from all extant Lepidoptera,but one genus(Agathiphaga, Agathiphagidae),in retaining four median veins in the forewing,a plesiomorphy also present in many Trichoptera. Evidence for placing Mesokristensenia in the Lepidoptera includes four traits,notably a previously unrecorded autapomorphy of this insect order:beyond stem M1+2,vein M1 is bent and connected to cross-vein r-m(in both wing pairs).Among 24 characters taken into account to assess the systematic position of Mesokristensenia,12 are considered informative for a cladistic analysis involving this fossil taxon and the four suborders recognized in present-day Lepidoptera(Zeugloptera,Aglossata,Heterobathmiina,and Glossata). 相似文献
15.
G.H. Shi 《Geomechanics and Geoengineering》2014,9(2):80-96
Continuous computation and limit equilibrium computation are the two independent computations for practical rock engineering. For global stability analysis, limit equilibrium is still the fundamental method. For any numerical method, reaching limit equilibrium requires large displacements, discontinuous contacts, precise friction law, multistep computation and stabilised time-step dynamic computation. Therefore three convergences are unavoidable: convergence of equilibrium equations, convergence of open-close iterations for contacts and convergence of the contact forces of dynamic computations. This paper utilises mainly two dimensional discontinuous deformation analysis (DDA) and an available simple version of three dimensional DDA. The applications show DDA has the ability to reach the limit equilibrium of block systems. 相似文献
16.
苏里格气田储层含水特征与测井识别方法 总被引：1，自引：0，他引：1
鄂尔多斯盆地苏里格气田盒8、山1气藏为弹性驱动的河流相低效气藏,储层非均质性强,压裂试气部分井出水。根据测井响应特征及非均质性将气层含水情况分为束缚水、层间水、滞留水3类,分析了3类含水气层特征,并在天然气测井响应机理研究的基础上提出了侵入分析与感应侧向联合解释法、分区图版法及气测综合判识法等气水层判识技术,使该地区气层测井解释符合率从70%左右提高到80%以上。 相似文献
17.
Generic distinguishing characteristics and stratigraphic ranges of fossil corallines: An update 总被引：1，自引：0，他引：1
P. Kundal 《Journal of the Geological Society of India》2011,78(6):571-586
Corallines or coralline algae are carbonate secreting and strongly calcified red algae of the order Corallinales of division
Rhodophyta. Architecturally, the corallines have two groups, the nongeniculate and geniculate coralline forms. Corallines
are used as a potential tool for paleoecology, paleoenvironments and paleobathymetry. Coralline algae are builder of porous
and permeable carbonate reservoir rocks for hydrocarbon and reefs rich in hydrocarbon. The old approach, ca. prior to 1977,
of taxonomy of fossil coralline genera has been replaced by the modern approach that established during the last decade using
certain distinguishing features such as arrangement of basal filaments, cell fusions, conceptacle perforations and orientation
of filaments around conceptacles of living corallines. The earliest confirmed fossil record of coralline algae is from the
Hauterivian (Early Cretaceous) and from the Hauterivian to the Pleistocene 9 nongeniculate coralline genera, namely Distichoplax, Lithophyllum, Lithoporella, Lithothamnion, Mesophyllum, Neogoniolithon, Phymatolithon, Spongites and Sporolithon and 7 geniculate genera, viz. Amphiroa, Arthrocardia, Calliarthron, Corallina, Jania, Metagoniolithon and Subterraniphyllum having different stratigraphic ranges are unequivocally known as fossils. After 1977, we do not have a comprehensive publication
giving the generic distinguishing characteristics and stratigraphic ranges of both nongeniculate and geniculate corallines.
The present paper gives an update of distinguishing characteristics of fossil coralline algal genera and their stratigraphic
ranges. 相似文献
18.
鄂尔多斯盆地吴旗地区长6储层孔隙结构特征 总被引：7，自引：0，他引：7
孔隙结构研究是油藏精细描述、储层综合评价的重要内容,采用铸体薄片、扫描电镜、铸体图像分析、高压压汞和恒速压汞等多种技术手段,对鄂尔多斯盆地吴旗地区长6储层的孔隙结构进行了深入分析和研究.鄂尔多斯盆地吴旗地区长6储层具有高孔低渗的特征,储层以原生剩余粒间孔为主,长石、岩屑及早期碳酸盐胶结物的溶解是形成次生孔隙的主要原因.中孔和小孔是油气的主要储集空间,细喉和中喉则是长6的基本渗流通道.铸体薄片、孔喉图像分析表明,吴旗长6储层具有复杂的孔喉分布特征,不同微相孔喉分布及孔隙结构特征是造成油井产能差异的重要因素. 相似文献
19.
针对动态规划在供水库群优化调度中存在"维数灾",且难以获得真正最优解这一缺点,将改进的加速遗传算法应用到供水库群的水资源优化配置之中。在加速遗传算法中,嵌入局部搜索,以加强算法的全局寻优能力。以库群间的水利联系为线索,设计了相应的算法框架,并提出了供水策略区间的概念。为了体现该算法的优越性,以二个串联供水水库的水资源优化配置为例,选用该方法与基于动态规划的轮库迭代法进行比较研究。结果表明该方法合理可行、收敛速度快,有一定的实用性。 相似文献
20.
莺歌海盆地地层各向异性多波地震判别技术研究 总被引：1，自引：0，他引：1
充分利用中国在海上采集到的多波地震资料:PZ分量(P波)时间偏移剖面、X分量(P-SV波)时间偏移剖面和Y分量(P-SH波)时间偏移剖面,对莺歌海盆地3个构造(A构造、B构造、C构造)和D砂体的地下岩石介质的各向异性特征进行了研究,Y分量(P-SH波)、X分量(P-SV波)的旅行时间闭合差、准各向异性系数和泊松比结果表明A构造、B构造、C构造等存在不同程度的各向异性,且A构造的各向异性最强.实践证明,在海洋石油勘探中,多波地震资料用于地下岩石介质各向异性的判别是可行的. 相似文献